Why AO Smith Water Heater Won’t Light Or Stay Lit [Solved]

Your ao smith water heater won’t light or stay lit because of the leading reasons. They are:

  • Insufficient gas supply
  • Faulty pilot light or bad Igniter 
  • A bad thermocouple 
  • A blocked tube
  • A defective pressure switch, and so on.

However, before replacing anything, first, try resetting your heater and cleaning your AO Smith water heater pilot light to fix the heater lighting issues.

AO smith water heater won't light

Even then, if you struggle to fix it, we have identified each culprit that prevents your heater from igniting and shown their effective solutions. So, follow our well-proven guide and resolve the heater, not the lighting issues.

AO Smith Water Heater Won’t Light Or Stay Lit [Reasons + Solutions]

In this section, we will break down every reason behind your AO Smith water heater won’t light that you need to know to solve your problems. Let’s get started right here.

Note: You can also read how to fix the AO smith water heater won’t stay lit.

1. Gas Supply Issue

An improper gas supply is mainly responsible for not lighting your water heater. Your AO Smith water heater won’t ignite if the unit doesn’t get enough gas supply. Because a proper gas supply ensures your water heater lights up. So, without gas, a status light will never stay lit, let alone operate your water heater.

In this case, if the gas valve is in the off position, the unit will receive no gas. Besides, the light won’t come on if there is any air in the gas supply line and pilot tube. As a result, you can’t expect the pilot to flash or blink.


First, make sure the gas valve is in the ON position. If it remains in the off position, clock it to the ON position to allow the gas supply to the unit. You should follow the lighting instructions on the heater’s label on how to light.

Second, purge the pilot light tube and gas line to bleed the air. To do so, push the control knob and hold it down until the pilot light comes back on or stays lit. You may need to repeat the process until you get a status light on your heater. 

Note: If your problem doesn’t resolve yet, check out the pilot light as it works as a push-button igniter.

2. Faulty Pilot Light

A faulty pilot is the next major factor behind the AO Smith gas water heater, not lighting. Basically, a pilot light makes sure to ignite the gas burner. So, your water heater won’t heat if the pilot light doesn’t ignite, 

AO smith water heater faulty pilot

Sometimes, there may be a buildup of carbon deposits on the pilot that protects the pilot as it doesn’t get enough combustion air. So, without lighting the pilot, the water won’t heat.


First, make sure the weather has any restrictions to light up the pilot.

But, if it gets restricted to the pilot in any way, try your best to clear it out with a stiff brush or compressed air. 

Next, turn the gas supply off to your heater and leave it for at least 10 minutes to cool down before attempting to relight it. 

But cleaning doesn’t bring any luck, replacement will be the best reply to fix your lighting problem. Whatever, you should try to relight your heater.

How To Relight Your AO Smith Water Heater

Once you have completed your cleaning and repairs, you can relight your AO Smith water heater by following these instructions:

First, turn the gas supply off to your heater and leave it for at least 10 minutes to cool down before attempting to relight it. Adjust the thermostat temperature to the lowest setting.

  • Place the gas control knob in the pilot position.
  • Press down on the Red Pilot Set button to send gas to the burner assembly.
  • Hold the Pilot red button gently until you hear a “click” sound, and the pilot light returns. 
  • You may need to press the button a couple of times until the pilot lights come on.
  • Release the button. Set the button slowly after the pilot is lit, then let the thermocouple heat up.
  • Turn on the gas control valve.
  • Replace the back access panel on the back of the water heater.

Finally, set your ambient temperature.

3. Defective Igniter

Your AO Smith water heater pilot light won’t stay lit due to the failure of ignition. To stay lit, it is essential to have enough voltage with the igniter.

Ao smith water heater defective igniter

But when the voltage is fine, but it doesn’t glow, this warns that the ignition is defective. 


First, ensure the igniter is getting sufficient voltage. If it gets the right voltage, the igniter will work fine. And then, surely, your burner will stay lit. Otherwise, your ignitor is defective and should be replaced immediately.

4. Electrode Sparking Problem

The AO Smith water heater won’t spark if there is an issue with the spark electrode. This may happen because of a broken or defective electrode or anode rod.

Ao smith water heater electrode sparking problem

Basically, the spark electrode allows an intermittent high voltage to light the pilot flame. You won’t see any spark there if the electrode or anode rod gets faulty or worn out.

Plus, over time, the pilot light electrode tip may be obstructed by carbon deposits, dirt, and rust that restrict the igniter from releasing the sparks. So, the pilot light won’t ignite because of this lack of sparks. 


  • Firstly, start your inspection with the wire connections of the igniter and see if the igniter is getting enough voltage. If there are any faulty connections, reconnect them and tighten them up. Hopefully, the tips will solve the issue.
  • If reconnecting the igniter wires fails to get the expected result, turn off the gas valve and remove the access panel to get to the burner assembly, and pull it out.
  • Look through the window to determine whether there is a small spark igniter with the burner.
  • Ensure the electrode or pilot light is fully clean and doesn’t get damaged. If not so, you can use an emery cloth or a stiff brush to clean any debris from it.
  • Hold and press the piezo igniter to light it. Yet if the igniter can’t produce any spark, then the anode rod has gone bad.
  • If you can’t clean it, you have to replace the heater’s faulty electrode and igniter parts as soon as you can.

5. Defective Thermocouple

A faulty thermocouple is another culprit for your AO Smith water heater burner won’t stay lit. Basically, the water heater thermocouple is considered the brain of the water heater.

ao smith water heater defective thermocouple

A thermocouple detects heat on the pilot flame and allows your heater to turn on. But when it gets bad, it shuts off the gas both for the pilot light and the burner.

So, it’s a clear sign to you that the flame can’t heat the thermopile sufficiently. Besides, the pilot and the burner won’t be able to ignite unless the thermopile reaches its operating temperature.

On the other hand, you will face the following problems due to the bad or broken thermocouple. For Instance;

  • The pilot light is on the Smith Water Heater, but the burner won’t stay lit.
  • Once lighted the pilot, but it went out when you released the control knob.
  • The status light won’t come on for 90 seconds after the pilot light operation.

However, let’s know how to solve the problems.


  • To fix it, first, turn off the gas valve and remove the access cover. Let the unit cool down for 10 minutes to cool your thermocouple.
  • Then, locate the thermocouple. Examine it to see if it gets clogged or bad.
  • Pull out the thermocouple with a screwdriver.
  • Ensure the thermocouple has no rust. If it gets rusty, clean it with sandpaper and scrape off the dirt so that the pilot gets enough ventilation.
  • Try to relight the pilot by following the manual lighting instructions on the water heater’s label. If you fail to light it, then replace the thermopile.
  • If these steps for heater thermocouple cleaning can’t solve the issue, there may be a problem with its bent or defection. And it is no longer functional as it won’t be able to sense the heat.
  • But if you notice the thermocouple is bent or bad, it would be best to replace the broken thermocouple.
  • You can watch the below video on how to replace a thermocouple without calling for help from a plumber.

6. Blocked Pitot Tube

A blocked or dirty pilot tube is the next reason for having no status light with the AO Smith water heater. Your water heater won’t ignite because it’s being blocked by dirt, dust, and debris that restricts the flow of gas from the pilot tube. It ensures a spontaneous flow to the burner and pilot light functionality.

But when you cannot ignite as usual, it means that the pilot light is not getting the proper fuel to ignite at all.


When your pilot tube gets dirty, take a long needle and poke it through the pilot hole to clear out debris from there. Repeat the process as required to remove the dust and debris that has accumulated there.

To make sure it has been cleaned, try to relight the pilot to see whether the pilot blinks a bright or blue flame. Hopefully, the tips will fix the problem.

7. Defective Gas Valve

When either cleaning the pilot light or replacing the thermocouple doesn’t help ignite your water heater, the issue might be with the defective gas control valve. 

Because the gas control valve is an essential element that measures the amount and pressure of a gas as needed in the unit and allows the pilot to stay lit. 

ao smith water heater defective gas valve

And then, the lighted pilot heats the thermocouple that delivers a signal to the gas valve to operate the burner in order to heat the water.

Unfortunately, if the control valve doesn’t get the signal, it cannot produce the right amount of gas. So,  it won’t allow your heater to heat and stay lit. This may happen if the gas valve gets defective or broken. 


To solve the gas valve issue, just disconnect the gas lines. Then you will need an adjustable wrench to disconnect the lines. Now, install a new gas control valve into your AO water heater, as this part is not a serviceable unit at all.

How To Replace Ao Smith Water Heater Gas Control Valve

  • Turn off the gas supply valve.
  • Disconnect the lines, such as the igniter, pilot tube, thermal switch, or thermocouple from the gas control valve.
  • Use a threaded pipe to detach the gas control valve.
  • Replace a new valve, reconnect control valve port connections, and turn on the gas supply.
  • Make sure there is a perfect balance between the gas and the air supply. Finally, your lighting issue will be solved. 

If you aren’t inclined to replace it, call a professional plumber to reinstall it safely.

Note: Be alert. Too much gas flow can cause fires and explosions.

8. Faulty Pressure Switch

A faulty pressure switch is a culprit that prevents your electronic water heater pilot light from lighting. It works as a safety feature on the heater that detects the negative pressure produced by the draft motor.

ao smith water heater faulty pressure switch

When the proper combustion/airflow is received, the switch closes and signals the control board to run the ignition procedures.

But if the pressure switch is defective or faulty, the ignition process will stall and the heater won’t light at all.


To solve the pressure switch issue, don’t forget to measure the voltage using an ohmmeter because a defective switch may leave a high voltage.

For the broken switch, it is wise to replace the malfunctioning pressure switch by installing a new one.

9. Damaged Gas Burner

If all attempts cannot light the heater, it comes to the point of the damaged gas burner. And you can’t expect a light with your AO Smith water heater.

Plus, this may occur because an old water heater or the main burner chamber may have cracked. Unfortunately, your water heater has reached an extremely old age.


You may have to change the entire burner assembly, as it is quite impossible to repair. So, it would be wise to replace the gas burner ASAP.

10. Improper Installation

A faulty installation is also a cause for your new AO water heater not to turn light. Your heater’s light won’t come on if:

  • You don’t turn the manual gas valve to the ON position.
  • Lack of air in the pilot tube and the gas supply line.
  • Ignition procedures don’t work properly.


Make sure you have set the gas valve in the right position; otherwise, no gas will flow to the burner chamber for combustion.

Next, check for sufficient air from the pilot tube and the gas supply line. To inspect it, press the control knob to let air flow.

Finally, investigate to see if the ignition is sparking well. To inspect the ignition process, have a sharp eye on the electrode or anode rod. You’ll see a spark from there.

Note: If you are not good at installing the heater, call a professional to install it properly. 

How To Reset Your AO Smith Water Heater

When you are struggling to ignite your AO Smith water heater, before going to any maintenance or repair, first try resetting it. Because resetting may solve most of your lighting-related problems.

ao smith water heater

So, follow these 6 effective steps to reset your AO smith water heater.

Step 1: Take your adjustable screws/tools. Go to the electric panel, find the breaker, and flip it to the off position.

Step 2: Remove the screws that hold the cover in place by opening the cover panel.

Step 3: Look for the reset button beneath the metal cover near the center of the unit. It may be hidden under a protective material (insulation). You’ll get a “Reset” button near the thermostat.

 Step 4: Simply press the reset button. After pressing on it, you’ll hear a ‘click’ sound that shows your heater has been reset to the point.

Finally, return to the electric panel and turn the breaker switch to ON.


What is a water heater pilot light?

A pilot light is an essential flame part of a water heater. It provides a flame to light, including the gas, the main burner, and various heating elements, and produces heat. Finally, your heater runs smoothly.

Does the AO Smith water heater pilot light stay lit all the time?

A gas water heater has a small flame (called a “pilot light”) to ignite the burner. The pilot light ignites the burner to heat the water. So, it is normal to stay light all the time.

If the pilot light isn’t lit at all, your heater won’t be able to keep warm water and instead will experience cold water. Because cold water is a sign that the pilot light has gone out. So, fix it ASAP.


Fortunately, we have already figured out the culprits that are responsible for your AO Smith water heater won’t be light and providing simple solutions.

So, whenever you face any lighting issues with your AO water heater, the above well-proven guide will definitely be effective for you to solve the issues by yourself.

Yet, if you have questions about the ignition issue, let’s know in your comments. We will reach out to you with a possible solution ASAP.

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